My brake lights wont work but the bulbs are good i can turn on the light theyll come on

also my headlights wont work unless i switch on the high beams.

any help would be great

 

I have a similar issue with my 75 Chinook. The rear driver side brake light, reverse, and plate lamp do not work. I don't even know where to begin with this. Short somewhere I imagine. I got a multimiter but don't really know the right way to use it.

Any ideas or suggestions?

 

Any trailer light connector/adapter on the truck? If so, remove it and see if the problem goes away.

Headlights:
- http://www.4crawler.com/4x4/CheapTri...eadlight_Combo

And might have a loose ground connection at the rear brake light socket. If so, brake and running light will be floating and might find ground via the other filament (1157 dual filament bulb).

 

Okay, I will continue to look for a loose ground. The thing that makes it a little more confusing for me is that since it is a Chinook conversion, when it was built they kind of did their own wiring. I've got cut wires and wires that branch out for side markers and such. I think the trailer light option was pretty standard because my '76 and '77 both came with the plug. It being a motor home, they removed that. Ther is no plug, but cut wires from the driver brake light.

I would really like to know what the setting needed for the multimiter is to find loose grounds and continuity.

Thanks.

 

Depends on the meter. If you have a continuity setting or beeper you could use that, or else use the lowest ohm range:
- http://www.4crawler.com/4x4/CheapTri...oUseAnOhmMeter

Even better is a test light as you'll use a decent amount of current to test the circuit, unlike a meter than uses almost no current. If you don't have a test light, easy enough to make one out of a spare 12 volt bulb and some wire, or a small flashlight bulb and a small battery or two. The tricky part with a loose ground or connection is that an ohm meter might show nearly 0 ohms (good connection), albeit measured at a tiny micro-amp current. But if you try and push a couple of amps (like a brake light pulls) through that same connection, it is no good. So the test light gives a more "real world" test.

 

Awesome, I'll give the bulb a shot this weekend. If there is a loose ground somewhere couldn't I just start another one?

I'm totally in the dark about electrical things. If there is power running to the light(s) couldn't I tap the pre-existing ground wire and find a new location ( assuming it is a loose ground.)?

 

Sure, but it depends on where the bad connection is. For example, see below for some fixes I had to do on my VW:
- http://www.4crawler.com/Diesel/Cheap...#SocketRepairs

Had a good ground connection to the bulb socket, but the current path inside the socket was corroded.

You need power and ground to make a circuit. Think of hooking a wire to the battery "+" terminal. You can hold onto it, wave it all over and nothing happens. But touch the bare end of the wire to the battery "-" terminal and "sparks fly" (don't try this at home!). But the trick with bad connections (be it ground or power) is to find out where the bad point is and then fix that. So one way to do that is check at the light bulb socket, check power to ground inside the socket or at the base of the socket with the bulb in place. If you see less voltage across the bulb than across the battery, start working back towards the battery checking voltage across the circuit. Alternately, with the power off, you can use your test light or ohm meter to measure the ground (or power) wire resistance back from the bulb. Basic idea is to "divide and conquer", find a point where everything is OK (like the battery) and a point where it is bad (like the bulb socket), then go some point halfway between those two points and re-test. If the mid-point tests OK, then you have eliminated the half of the circuit between the mid-point and the battery and if the mid-point tests bad, you can probably eliminate the half of the circuit between there and the bulb socket. So divide the circuit in half a few times and you quickly narrow down to where the problem is.

Also need to make sure you have the right bulbs, some times folks jam a single contact (1156) bulb into a dual contact (1157) socket. With force, it'll fit but may either not work at all or will short the brake and running light circuits together with uncertain results. And bulbs can look OK but be shorted or open internally, so you could actually test the bulb out of the socket to make sure it is OK.